1. Field of the Invention
The present invention relates to a drive detection device for a fixing device mounted on image forming apparatuses such as a copying machine, a printer, and a facsimile, and, more particular to a drive detection device for a fixing device employing an induction heating system.
2. Description of the Background
In recent years, there is a fixing device of an induction heating system used in image forming apparatuses such as a copying machine and a printer of an electrophotographic system. The fixing device includes a fixing member in which a metal layer having a small heat capacity is provided on the surface of an elastic layer thereof. When the metal layer is induction-heated in a state in which the fixing member is stopped, there is a risk that the fixing member overheats. Therefore, for example, JP-A-2006-26733 discloses a fixing device in which a rotation detection pattern formed by a thin-layer metal piece is provided in a fixing member. When the fixing member is rotated, the fixing device detects fluctuation in an induction load of an exciting coil periodically generated by the thin-film metal piece to thereby detect the rotation of the fixing member.
However, in the apparatus in the past, a new member, i.e., the thin-layer metal piece is necessary in the common fixing member. During the detection of the rotation, when a driving frequency of the exciting coil that performs induction heating fluctuates, there are fears that the induction load that should be detected also fluctuates, and accurate and quick rotation detection is not realized.
Therefore, there is a demand for development of a drive detection device for a fixing device that accurately and quickly detects a rotation state of a heat generating member, which has a metal layer on the surface of an elastic layer, to thereby prevent overheat of the heat generating member, which is caused by failure of detection or a delay in detection of the rotation state of the heat generating member, and realize improvement of safety.